The key connects Mono to Gemini
Mono uses your Gemini API key when it sends caption context to the Gemini model you selected for translation.
The key stays on the Chrome profile
The Chrome companion stores the key locally on the current Chrome profile so it can survive a browser restart without being synced as part of your Mono Workspace.
Pro access and Gemini access are different things
A valid Gemini key does not unlock Mono Pro. Trial or Pro entitlement controls whether the translation workflow can run. Gemini access only provides the AI model connection.
You can remove it any time
The extension includes a remove-key control. If you remove the key, Mono can keep your account and Workspace but cannot start a new Gemini translation until another valid key is connected.